Detection of carbon monoxide from biological tissue using difference frequency generation in periodically-poled lithium niobate near 4.6 μm

A mid-infrared gas sensor using difference frequency generation was developed to measure trace levels (similar to ppb) of biological carbon monoxide (CO). A periodically-poled lithium niobate crystal is pumped by a continuous wave Ti: Sapphire laser and a compact diode pumped Nd:YAG laser operating at 864.86 and 1064.6 nm, respectively. The strong infrared transition R(6) at 2169.2 cm(-1)(4.61 mu m) is chosen for convenient CO detection without interference from other gas species. Carbon monoxide is collected and flowed into a multipass cell with an effective optical path length of 18.3 m. Using such an experimental arrangement, we detected the generation of CO at levels of 30 ppb during a 30 min period from living vascular smooth muscle cells (1 x 10(7)) in basal state.